The present invention relates generally to a method and system of detecting the configuration of very small three-dimensional objects such as soldered portions or mounted parts on printed circuit boards, and more specifically, to a configuration detecting method and system which can eliminate noises resulting from the secondary and tertiary reflections on a surface of an object to be checked.
A recent tendency of semiconductor techniques is to increase the packing density of electronic parts to be mounted on a printed circuit board. As the semiconductor techniques advances, it has been demanded to develop the associated techniques. In respect of product quality control, in particular, the development of inspection techniques is indispensable.
An example of a prior-art configuration detection will be explained with reference to FIG. 1 in the case where electronic-part soldering portions on a printed circuit board are to be inspected.
In FIG. 1, leads 2 for an electronic part 1 are soldered onto respective lands 4 formed on a printed circuit board 3. For inspection of the configuration of such soldered portions, there has been, so far, used a light section method wherein, as shown in FIG. 2, a slit-shaped bright light is projected onto the soldered portions from a slit projector 6 disposed above the soldered portions so that an image detector 7 disposed obliquely at an angle with respect to the projected light can detect the configuration of the checked portions.
In the conventional method, as illustrated in FIG. 3, the detector 7 detects the image of the projected slit light segments 8 to 12 in the form of light section image of a three-dimensional object, whereby the configuration of the checked object can be determined.
However, if the objects to be checked have mirror or glossy surfaces as in the case of the illustrated soldered portions, then the slit bright light will be reflected on such surfaces. For example, in FIG. 3, the slit light segment 8 is regularly reflected on a soldered fillet portion 5, whereby the reflected light 13 is undesirably detected as if it were an actual slit bright light. Similarly, numeral 14 is a regularly reflected light of the slit light segment 12. Further, in the case where objects to be checked have mirror or glossy surfaces, it may also happen that the slit light segments 9 and 11 become darker than the reflected lights 13 and 14.
As a result, the prior art has such a defect that it is impossible to obtain a real light section image because of such abnormal reflections.